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S6 ALASKAN GLACIER STUDIES
lake water. In the outer portion of the area covered by the expanded glacier, a dense growth of mature alder and some cottonwood covers the overridden gravels, but the growth rapidly decreases in amount and density toward the present glacier fronts. In Seal Bay and Nunatak Fiord there are only scattered individual plants, and the density of alder growth gradually increases thence toward the portions of the inlet where the expanded glaciers ended. In other words, this period of ice advance was so recent that only a part of the area is as yet occupied by vegetation (PI. VI), and the outer portion is occupied only by the advance growth of alder and, in the extreme south, of cottonwood. The spruce forest of the Alaskan coast has not yet had time to advance upon the region from which the glaciers have so recently receded.
Recent Recession of the Glaciers. In Professor Russell's visits to the Yakutat Bay region in 1890 and 1891 he found the glaciers to be in general in a state of recession. Dr. Gilbert's observations in 1899 led him to the same conclusion, and our observations in 1905 showed that the glaciers were still wasting away. The evidence of this condition of recession is partly inferred from the characteristics of the glaciers and the conditions at their borders, and partly observed by direct comparison at the later dates "with observations made during the earlier studies. Russell, Gilbert, and the authors of this book, have all noted the fact that many of the glaciers are covered by ablation moraines at their lower ends, and that in some of the more stagnant portions these ablation moraines bear forests. From this condition the inference is perfectly warranted that the glaciers in these regions are wasting. More specific, however, is the evidence around the glacier borders, both at the sides, and, in those which end on the land, at their fronts. While forest, or at least alder (PI. VI, B), extends nearly up to the front of many of the glaciers, aoid also grows on the valley sides above them, there is, near many of the glaciers, a zone in front of and just above the glaciers, which is barren of vegetation (PI. VI, A). From such a condition one infers with certainty that the ice has withdrawn from such areas so recently that vegetation has not yet had time to encroach upon it. The extent of shrinkage indicated by this class of evidence varies with different glaciers, but it was present to some degree in the neighborhood of almost all the glaciers studied, and in some it indicates a great and long-continued shrinkage. This is particularly true in Nunatak and Russell Fiords, as already stated in the preceding section. Here it is certain that in the last century the recession has amounted to many miles.
By the photographs taken by Professor Russell, though they -were taken merely as incidents in a work of different object, a basis was established for future record of the changes in the position of the fronts of some of the glaciers; and still further basis for such comparative work was established by the photographs of the Canadian Boundary Commission in 1895. Naturally, therefore, Dr. Gilbert instituted such comparisons when, in 1899, he visited the region as a member of the Harriman Expedition; and he added a new basis for future comparison by taking photographs of still other glaciers. We, in 1905, therefore, had a body of photographic evidence upon which to study the changes of positions of the glacier fronts during recent years. Thiis study of photographic records shows that some of the glaciers, notably Hubbard and Turner, changed but little between 1891 and 1905, but that Nunatak and Hidden Glaciers receded greatly between 1899 and 1905. For the smaller glaciers there is no photographic basis for a state-men^ though the other evidence gives conclusive proof of recession in many cases.
In 1899 the Harriman Expedition added still another basis for future studies of the